In the systems studied thus far, the attachment of ruthenium- pentaammine to purine bases is governed by rate of the reaction. A different affinity pattern can be expected in a system governed by equilibrium processes. Equilibration becomes possible when the metal ion is labilized, as is the case when the sulfate group is attached to ruthenium(II). The interaction of trans- tetraammine- aquiosulfito- ruthenium(II) with purine bases will be investigated, as well as with some of the biologically important molecules to be mentioned. To apply ruthenium ammines in protein chemistry, basic information on the properties of molecules which bind to the metal is needed. The interaction of (Ru(NH3)5H2O)2 ion and of trans-(Ru(NH3)4(SO3)H2O) with amino acids bearing the functions H-S-R, CH3-S-R, NH2-R and proline and histidine will be studied. Current work on reactions of amino acid esters, nitriles and amides as they are affected by coordination to ruthenium(II) and ruthenium(III) will be continued. The work on ruthenium-sulfur combinations will be extended to a search for micron-S and bis(micron-S) diruthenium combinations and a study of their oxidation-reduction properties.